This application is based on application No. 99-1633 filed in the Korean Industrial Property Office on Jan. 20, 1999, the contents of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to a lithium secondary battery, more particularly to a lithium secondary battery wherein an electrolyte-injecting hole is formed at the cap area and is plugged by a sealing member.
(b) Description of the Related Art
As the use of portable electronic devices has been rapidly increasing of late, the consumption of batteries used as power sources for these is also escalating. Secondary batteries that are not discarded after they are discharged but which can be charged and discharged repeatedly are the main battery used for the above application.
A main type of secondary battery currently being researched and developed is a lithium ion secondary battery, which attracts attention from the related industries due to its many advantages, such as large capacity, good stability, and long cycle life.
Although batteries are generally made in a cylindrical shape, as portable electronic devices are gradually miniaturized and being made thinner, prismatic shaped batteries are being developed and manufactured. The production of lithium ion secondary batteries is also following this trend.
FIG. 4 is a sectional perspective view illustrating a general prismatic lithium ion secondary battery in which a polar plate set (3) comprising an anode plate, a cathode plate, and a separator is inserted into a can (1) which plays the role of a cathode terminal. An open part of the above can (1) is sealed by a cap (7) containing an anode terminal (5), and a safety device is installed inside the anode terminal (5).
The polar plate set (3) is first inserted into the can (1), the cap (7) is put on an open part of the can (1), and the joining surface areas thereof are affixed by laser welding in order to manufacture a prismatic battery. Thereafter, an electrolyte is injected into the can (1) through an injecting hole (7a) formed at one side area of the cap (7). As shown in FIG. 5, in the conventional art the above injecting hole (7a) is sealed after the electrolyte has been injected, the sealing method consisting of the insertion of a ball member (9) comprised of aluminum, etc. into the above injecting hole (7a), and a separate thin metallic plate (11) is placed over the ball member (9), completely covering the above injecting hole (7a), and affixed to the above cap (7) by laser welding.
As the area surrounding the injecting hole (7a) is contaminated to a certain degree when electrolyte is injected through the above injecting hole (7a), it is possible for the electrolyte to leak into a gap between the above injecting hole (7a) and the ball member (9), and this leaked electrolyte can affect the thin metallic plate (11). There have been cases where the sealing of the injecting hole (7a) has deteriorated since the welding was poorly made due to leaked electrolyte when the above thin metallic plate (11) is welded to the battery cap (7). Furthermore, the state of the battery can be degraded due to electrolyte leakage and unnecessary internal gas leakage from a poorly sealed injecting hole (7A).
The present invention is invented taking into account the above problems, and it is an object of the present invention to provide a lithium secondary battery that prevents electrolyte and internal gas leakage by durably sealing the electrolyte injecting hole.
Therefore, the present invention provides a lithium secondary battery comprising as follows:
a) a can having an internal space;
b) a polar plate set comprising an anode plate, a cathode plate, and a separator which is installed by being inserted into the above can;
c) a cap assembly having an electrolyte injecting hole which seals the can interior by being mounted on an open part of the can; and
d) a sealing member for an electrolyte injecting hole comprised of an inserting part and a head part which is inserted into the above cap assembly through the above electrolyte injecting hole and affixed to the above cap assembly.
The above sealing member for electrolyte injecting hole which is formed in a rivet-like shape is affixed to the above cap assembly by laser welding.